Browsing by Author "Herber, Daniel R., committee member"

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Open Access
Cislunar system of systems architecture evaluation and optimization
(Colorado State University. Libraries, 2023) Duffy, Laura, author; Adams, Jim, advisor; Sega, Ronald M., committee member; Herber, Daniel R., committee member; Fankell, Douglas, committee member
Cislunar space is the next frontier of space exploration, but a sustainable architecture is lacking. Cislunar space is considered a complex system of systems because it consists of multiple independent systems that work together to deliver unique capabilities. The independent systems of the cislunar system of systems include the communications, navigation, and domain awareness systems. Additionally, the methodology to design, evaluate and optimize a complex system of systems has not been published. To close the gap, a comprehensive needs analysis is performed for cislunar space. Next, model-based systems engineering is used to design the cislunar system of systems. The cislunar architectures are designed in terms of constellations and payloads. The architectures are each evaluated in terms of cost and performance. An appropriate optimization algorithm is found for the system of systems, and the results of the optimization are evaluated using multiple techniques for comparison. A literature review is included on the topics of cislunar architectures, system of systems, model-based systems engineering, system architecture evaluation, and system architecture optimization. During the research of cislunar architectures, a needs analysis is completed which identifies the three primary missions planned for cislunar space and eight supporting functions to provide the infrastructure for the primary missions. The primary missions identified include science, commerce, and defense. The eight supporting functions identified include transportation, communication, domain awareness, service, energy, shelter, and control. Technologies and programs are identified for each supporting function, included gaps in needed technology or programs. For the evaluation and optimization of the system of systems, the supporting functions are down-selected to include only the three necessary supporting functions for any operations in cislunar space: communications, navigation, and domain awareness. A system architecture is developed using Systems Modeling Language in Cameo Systems ModelerTM. The model is designed using the Model-based Systems Architecture Process which includes the design of the Operational Viewpoint, Logical/Functional Viewpoint, and Physical Viewpoint. The Operational Viewpoint includes structural, behavioral, data, and contextual perspectives. The Logical/Functional Viewpoint includes structural, behavioral, data, and contextual perspectives. The Physical Viewpoint includes design, standards, data, and contextual perspectives. Each of these perspectives are represented in the form of Cameo Systems ModelerTM diagrams or tables. Diagrams include block definition diagrams, internal block diagrams, use case diagrams, activity diagrams, and sequence diagrams. Additional modeling concepts beyond the Model-based Systems Architecture Process are included in the Cameo Systems ModelerTM model and analysis of the model. These topics include allocating requirements, stereotypes, patterns in architecture decisions, architecture optimization, verification, validation, complexity, and open systems architecture. Cislunar constellations and payloads are designed which account for the cislunar physical environment. Six constellations are designed to be included in the optimization algorithm. These constellations include Lagrange light, Lagrange medium, Lagrange heavy, Earth-based, Earth plus Moon, and Earth plus Lagrange. These constellations essentially represent the location of the bus while the payloads provide the functionality of the system. Payloads are designed for the supporting functions deemed essential for a basic cislunar infrastructure, which are communications, navigation, and domain awareness. The optimization algorithm runs through each possible combination of payload and bus, including any opportunities to integrate multiple payloads on a single bus. The total number of possible architecture combinations for the optimization algorithm is 288. The payload sensors are modeled in Systems Tool Kit and evaluated for physical performance. Additionally, each payload and bus possibility are evaluated for cost using the Unmanned Space Vehicle Cost Model and professional estimates. The performance and cost metrics are used in the optimization algorithm. The optimization algorithm uses multi-objective optimization with an integer linear program. The result of the optimization algorithm is a pareto front of the highest-performance, lowest-cost architectures. The architectures along the pareto front are evaluated using multi-criteria decision making with and without evidential reasoning to find the "best" architecture. A Kiviat chart assessment is also performed, though this method is shown to not be practical for the cislunar application. The model and conclusions of the dissertation are validated using a variety of industry-accepted techniques. The cislunar architectures are validated via peer-review. The performance evaluations are validated via a validated physics model. The cost evaluations are validated by a validated cost-model when possible and by peer-review. The optimization algorithm is validated by comparison to a manual optimization method. The Cameo Systems ModelerTM model is validated using validation techniques internal to the tool. Suggestions for future work are presented. Future work could include fully integrating the Cameo Systems ModelerTM model with the Systems Tool Kit model, providing improved cost estimates, using alternative optimization parameters, adding supporting functions as they are identified, evaluating the architectures using additional metrics, evaluating additional constellations, applying integration at the functional level, or assessing non-homogenous requirements.
Open Access
Economic impact of thermal energy storage on natural gas power with carbon capture in future electricity markets
(Colorado State University. Libraries, 2022) Markey, Ethan James, author; Bandhauer, Todd M., advisor; Quinn, Jason C., committee member; Herber, Daniel R., committee member
As policies evolve to reflect climate change goals, the use of fossil fuel power plants in expected to change. Specifically, these power plants will need to incorporate carbon capture and storage (CCS) technologies to significantly reduce their carbon emissions, and they will be operated flexibly to accommodate the growing concentration of renewable energy generators. Unfortunately, most CCS technologies are very expensive, and they impose a parasitic heat load on the power plant, thereby decreasing net power output and the ability to operate flexibly. This research evaluated the economic potential of using hot and cold thermal energy storages (TES) to boost the net power output and flexibility of a natural gas combined cycle (NGCC) power plant with CCS capabilities. Resistively heated hot TES was used to offset the parasitic heat load imposed on the NGCC by the CCS unit while vapor compression cooled cold TES was used to chill the inlet air to the power plant. Thermodynamic models were created for the base NGCC + CCS power plant, the hot TES equipment, and the cold TES equipment, to determine key performance and cost parameters such as net power output, fuel consumption, emissions captured, capital costs, and operational costs. These parameters were then used to simulate the operation of the power plant with and without the TES technologies in accordance with fourteen electricity pricing structures predicted for different future electricity market scenarios. The difference in net present value (NPV) between the base NGCC + CCS power plant and power plant with the TES technologies was used as the primary economic metric in this analysis. The NPV benefit from increased revenue due to TES utilization was found to outweigh the NPV penalty from the additional capital costs. This positive economic result was attributed to the low cost of the TES equipment and the ability to charge the storages using cheap electricity from high levels of renewable output. The results have shown that hot TES increased NPV in 12 of 14 market scenarios while the cold TES increased NPV in 14 of 14 market scenarios. A combination of both hot and cold TES yielded the largest increases in NPV.
Open Access
Transient modeling of an ambient temperature source centrifugal compressor steam generating heat pump
(Colorado State University. Libraries, 2024) Ryan, Kelly Patrick, author; Bandhauer, Todd M., advisor; Windom, Bret C., committee member; Herber, Daniel R., committee member
As the US electricity grid transitions to renewable power generation, electrifying end-uses that are currently fossil fuel fired presents a promising path towards deeper decarbonization, and next generation high temperature heat pumps are a viable solution for decarbonizing fossil fuel fired steam boilers. These next-gen systems require a higher degree of design complexity and more finely tuned control strategies than existing systems, and therefore can benefit from complex transient modeling that has not been previously implemented for these types of systems. A transient study of a novel steam-generating heat pump with steam delivery temperature of 150°C was conducted using physics-based simulation software. The model used manufacturer supplied performance data to calibrate each competent, providing reliable preliminary validation to the model. The model was set up to match the configuration of a prototype system constructed at Colorado State University. It was found that the results of the transient model agreed well with the steady state model of the heat pump at the design point. Transient conditions including cold startup to full load operation, full load operation to part load operation, and part load operation back to full load operation were modeled and the system was found to operate with stability. Compressor and expansion valve performance was investigated. Compressors were found to operate within their performance maps for both steady and transient operation. A control strategy was developed for the expansion valves to prevent liquid ingestion when transitioning to turndown operation. The system COP was predicted for both full and part load operation and in transition between them.